The present invention relates generally to the production of electrical wire harnesses, and more specifically to a wire measuring apparatus that significantly reduces errors in measurement of the wires.
Many machines are known in the art for production of wire harnesses and those machines incorporate different apparatus for measuring wires. One apparatus is known for producing multiple wire harnesses and includes a plurality of wire supply reels that contain respective supplies of wire, a wire measuring device for measuring and feeding each such wire depending on the demand for the wires, guide means for guiding each of the wires downstream along the wire length, means for adjusting the pitch of the wires depending on the wire demand, a termination device for terminating electrical connectors to the opposing ends of the wires, and an ejection device for ejecting the completed harness.
The aforesaid wire measuring device is illustrated in FIG. 9 and includes a multiple roller assembly 101, 102, 103, 104 for each of the multiple wires 201, 202, 203, 204 used in the harness and includes the combination of a wire feed roller and a wire pressure roller. An electric motor is used as the means to drive each set of rollers in their respective rotation. A single drive motor is mounted directly to each pair of rollers. The size of these motors is bulky and therefore difficulty is encountered in arranging all of the required motors at the same position in the wire feeding direction. The narrow pitch of the wires is too small to permit the motors to be aligned in side-by-side order without causing interference between the casings of the motors and because the space in a direction transverse to the wire feed direction is limited.
Due to this interference problem, the wire drive motors are arranged in a staggered arrangement to avoid interference with each other. The measuring roller assemblies 101, 102, 103 and 104 for driving respective wires 201, 202, 203 and 204 are therefore arranged in a non-aligned, stepwise order as illustrated in FIG. 9. In such an arrangement, wire 201 has the longest length "A" between its corresponding wire measurement roller 101 and the outlet end 120 of the measuring device. Wire 202 has the second longest length "B" between its corresponding measurement roller assembly 102, while wire 203 has the third longest length "C" between its corresponding measurement roller assembly 103 and the outlet end 120. Lastly, the fourth wire 104 has the shortest length "D" between its corresponding measurement roller assembly 204 and the outlet end 120 of the measuring apparatus.
As an example of the deficiencies that occur in the use of the aforesaid wire measuring apparatus, it is assumed that wire 201 is fed in a length of 100 mm by its measuring roller assembly 101; wire 202 is fed in a length of 70 mm by its measuring roller assembly 102; wire 203 is fed in a length of 50 mm by its measuring roller assembly 103; and, wire 204 is fed in a length of 30 mm by its corresponding measuring roller assembly 104. The respective wires pass through the fore going wire guide means, a wire pitch adjusting device before being fed toward the pressure welding device. At this time, while each wire is fed through wire paths defined in the wire guide means, the wire pitch adjusting means and so forth with a certain clearance maintained between the wire and wall surface of the wire paths, each wire may encounter frictional forces due to contact with the walls and other surfaces of the wire path. If such frictional forces are exerted on the wires during the feeding thereof, the flexibility of the wires are likely to cause bowing or slackening during feeding.
The degree of bowing or slacking is most significant in the wire 201 that has the longest wire length "A" and is the least in the wire 204 that has the shortest wire length "D". Under these conditions, even when the respective measuring roller assemblies are driven accurately for times selected for feeding the respective lengths, i.e., 100 mm, 70 mm, 50 mm and 30 mm of the wires 201, 202, 203 & 204 by their corresponding respective measuring roller assemblies 101, 102, 103 & 104, the influence of interference between the wire and the peripheral surfaces of the wire paths that result in bowing or slacking by friction becomes most significant on the wire 201 fed in the length of 100 mm. Therefore, the feeding error in the wire 201 becomes much greater than that which may occur in wire 204. In each measurement cycle, greater measurement error tends to be caused in the wire having a greater feeding length than that in the wire having the smaller feeding length.
In view of the multiple wires that are processed in one cycle of the apparatus, greater error in the feed length should be caused in the wire having greater length than that having smaller length. Therefore, the magnitude of measurement error will fluctuate between the wires fed by the apparatus. Hence, correction of measurement error cannot be uniformly done and causes difficulty in correcting the measurement error.
Accordingly, the present invention is directed to a wire measuring apparatus in which errors of wire measurement are reduced.